This invention relates to delay lines for electrical signals and, more particularly, to electronically variable delay lines operable at microwave frequencies.
Delay lines are utilized in signal processing operations for adjusting the time of arrival of one signal relative to that of a second signal. The delay lines may be fabricated of digital circuitry or analog circuitry, and the delay may be fixed or variable. In the case of an electronically variable delay line of analog construction, the amount of delay can be varied by application of a voltage to a control terminal of the delay line. With respect to delaying a signal having a sinusoidal waveform, this being a frequent situation in microwave applications, the effect of the delay line is to impart a phase shift; thus, in this situation the delay line may be regarded as a phase shifter.
Numerous circuits are available for imparting delay electronically variable phase shifts but few for electronically variable delay.
Thus, a problem exists in that, while microwave signal processing techniques can benefit from the utilization of electronically variable delay lines and phase shifters, the available semiconductor circuits do not provide adequate capability.